tính nhanh 90:45+90:56+90
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A 12x56 + 12x44 =44+56=100
100X56=5600
b 45x12-45x2+45x90=90+2-12=80
80x45=3600
a) 12 x 56 + 12 x 44
=12.(56+44)
=12.100
=1200
b) 45 x 12 - 45 x 2 + 45 x 90
=45.(12-2+90)
=45.100
=4500
![](https://rs.olm.vn/images/avt/0.png?1311)
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a) 560 : 20 = 28 560 : 2 = 280 | b) 450 : 90 = 5 4 500 : 90 = 50 | c) 400 : 50 = 8 4 000 : 50 = 80 |
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90 - 19 - 11 - 45 + 55
= 71 - 11 - 45 + 55
= 60 - 45 + 55
= 15 + 55
= 70
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103 + 456 = 559
567 + 345 - 327 = 585
45 x 66 - 56 + 90 = 3004
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\(A=\frac{1}{3.4}+\frac{1}{4.5}+....+\frac{1}{9.10}=\frac{1}{3}-\frac{1}{4}+.....+\frac{1}{9}-\frac{1}{10}\)
\(=\frac{1}{3}-\frac{1}{4}+.....+\frac{1}{9}-\frac{1}{10}\)
\(=\frac{1}{3}-\frac{1}{10}\)
\(=\frac{7}{30}\)
\(A=\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}\)
\(A=\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\)
\(A=\frac{1}{3}-\frac{1}{10}\)
\(A=\frac{10}{30}-\frac{3}{30}=\frac{7}{30}\)
Vậy \(A=\frac{7}{30}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
ko tính được 90 :56 làm sao
90:45+90:56+90=90:(45+56+1)=90:102=15/17